(i) Field of the Invention
This invention relates to a pulse generator in which an inductive element and a nonlinear condenser are connected.
(II) Brief Description of the Prior Art
Regarding a pulse generator in which an inductive element and a nonlinear condenser are connected, there have hitherto been reported examples in which it is employed as a discharge lamp starter in a discharge lamp circuit for a fluorescent lamp, a high pressure discharge lamp or the like. In this case, an inductive ballast for the discharge lamp is used as the inductive element, and single-crystal BaTiO.sub.3 is used as the dielectric material of the nonlinear condenser. Since, however, BaTiO.sub.3 has a high melting point of 1613.degree. C., it is very difficult to grow the crystal of a size to be put into practical use. Accordingly, the prior-art pulse generator employing BaTiO.sub.3 is industrially impractical.
As is well known, a prior-art starter circuit for a fluorescent lamp for domestic use comprises in combination a glow lamp and a choke coil ballast as shown in FIG. 1. In the figure, numeral 1 designates a fluorescent discharge tube, numeral 2 a ballast, numeral 3 a glow lamp, and numeral 4 a condenser for preventing noises. Although the glow lamp in the circuit is inexpensive, it has the disadvantages (1) that the time required for lighting is as long as 3 seconds on the average, (2) that the life is as short as 2 to 3 years in the ordinary uses, etc. One of expedients for compensating for these disadvantages is the system which employs a nonlinear condenser instead of the glow lamp. FIG. 2 shows an example of the fluorescent discharge lamp circuit employing the nonlinear condenser. In the figure, numeral 5 designates a nonlinear condenser, and numerals 6 and 7 denote a silicon symmetrical switch (SSS) and a diode for a preheat circuit, respectively. The nonlinear condenser 5 exhibits a hysteresis characteristic as shown in FIG. 3a as to the quantity of charges Q versus the applied voltage V. The hysteresis characteristic is attained in such a way that the dielectric material portion of the condenser is made of a ferroelectric material. FIG. 3b illustrates the relationship between the capacity C and the applied voltage V of the nonlinear condenser which has the hysteresis characteristic as shown in FIG. 3a. When such nonlinear condenser is assembled in the circuit, the charges Q trace a course ABD in FIG. 3a with the increase of the applied voltage. This becomes as shown in FIG. 3b when observed as the variation of the condenser capacity. That is, a large capacity state B and a small capacity state D of the condenser are alternately realized at every half cycle on the hysteresis curve, and changes just as in case of bringing a switch into the "on" state and the "off" state occur. The variation can generate a high pulse voltage by abruptly cutting off a current flowing through the choke coil. Accordingly, the instant start is possible owing to this operation. The effect by the ferroelectric material as stated above is significant, not only in the circuit of the fluorescent lamp, but also in a circuit of a high pressure discharge lamp such as high pressure mercury lamp and high pressure sodium lamp. FIG. 4 shows an example in the case of employing the nonlinear condenser 5 for the high pressure sodium lamp. In the figure, numeral 8 represents a high pressure sodium lamp, and numeral 9 a ballast. Since the high pressure discharge lamp does not require the preheat as in the fluorescent lamp, the circuit becomes a very simple construction in which merely the nonlinear condenser is connected in parallel with the discharge lamp and the choke coil is incorporated on the power source side.